1. Field of the Invention
The present invention relates to an apparatus and process which enables to efficiently form a deposited film including a functional deposited film such as an amorphous semiconductor film usable in various devices such as semiconductor device, electrophotographic light receiving member, image-input line sensor, image pickup device and photovoltaic device, on a given substrate by way of plasma CVD process.
2. Related Background Art
In recent years, there have been proposed a number of deposited films comprising amorphous materials such as amorphous silicons, e.g., amorphous silicons in which dangling bonds are compensated by hydrogen atoms or/and halogen atoms, usable as semiconductors in semiconductor devices, electrophotographic light receiving members, image-input line sensors, image pickup devices, photovoltaic devices, or other electronic elements. Some of these deposited films have been practically using in these devices, members-or elements.
By the way, in the image-forming industrial field, for the photoconductive material to constitute a light receiving layer in an electrophotographic light receiving member, it is required to be highly sensitive, to have a high S/N ratio (photo-current (Ip)/dark current (Id)), to have absorption spectrum characteristics suited for an electromagnetic wave to be irradiated, to be quickly responsive and to have a desired dark resistance. It is also required not to harm living things, especially humans, upon use.
Particularly for electrophotographic light receiving members used in an electrophotographic apparatus which is used as a business machine at the office, causing no pollution is highly important.
From these standpoints, public attention has been focused on a-Si series light receiving members comprising amorphous silicon (a-Si) materials, for example, as disclosed in U.S. Pat. No. 4,265,991 which discloses an electrophotographic light receiving having a photoconductive layer constituted by an a-Si material and which excels in moisture resistance, durability, and electric and photoconductive characteristics.
Besides, U.S. Pat. No. 4,788,120 discloses an electrophotographic light receiving member having a surface protective layer constituted by an amorphous material containing silicon atoms, carbon atoms, and hydrogen atoms in an amount of 41 to 70 atomic %.
Based on these techniques, there has been realized a desirable a-Si series electrophotographic light receiving constituted by an a-Si material, which is satisfactory in electric, optical and photoconductive characteristics, use environmental characteristics and durability, and enables to provide a high quality reproduced image.
In order to effectively produce such a desirable a-Si series electrophotographic light receiving member, an advanced technique is required. Particularly, for an a-Si series electrophotographic light receiving member, it is necessary to have a greater area and thickness in comparison with other devices and because of this, not only to ensure uniformity but also to prevent abnormal film growth due to a nucleus comprising a foreign matter during the deposition of an a-Si film are important factors.
In view of this, there are various proposals for stably and efficiently producing a high quality a-Si series electrophotographic light receiving member on an industrial scale.
Incidentally, in the production of an a-Si series electrophotographic light receiving member, there has been pointed out the occurrence of a spherical growth defect which becomes a cause of entailing a defective image comprising a so-called xe2x80x9cminute blank areaxe2x80x9d on an image reproduced. In most cases, such spherical growth defect is considered to occur due to abnormal film growth based on a particle generated when a film deposited on a inner face of a deposition chamber is removed.
Separately, for an electrophotographic light receiving member produced by a conventional manner, there has been pointed out a problem in that unevenness in density is sometimes occurred for an image reproduced.
In order to solve these problems, there are also various proposals.
Specifically, for example, Japanese Unexamined Patent Publication No. 4183871/1992 discloses a deposited film-forming process using a microwave plasma CVD apparatus having a microwave introduction means with two different regions.
This document describes that by making the microwave introduction means to have a face, which is to be contacted with plasma generated upon film formation, such that has a value of 2xc3x9710xe2x88x922 or less in terms of a product of dielectric constant (∈) and dissipation factor (tanxcex4) with respect to the frequency of a microwave used, stable discharge can be caused while preventing a film deposited on an inner face of a deposition chamber where a deposited film having an improved uniformity and which does not entail a defect for an image reproduced. The publication illustrates a technique of coating a microwave introduction means with an alumina ceramic by way of a plasma spraying process. According to the technique described in the above document, it is possible to form a high quality deposited film with few spherical growth defects.
Now, in recent years, there is an increased demand for an electrophotographic apparatus which provides a high quality reproduced image at a high speed. In addition, there is an increased demand for the electrophotographic apparatus having reduced frequency of maintenance by improving the reliability of its constituents.
Particularly, in the production of a light receiving member produced by the conventional deposited film-forming apparatus, light receiving members are liable to entail a minute blank area due to the foregoing spherical growth defect or a minute black area on a reproduced image, depending upon the film-forming conditions employed. Further, depending upon the film-forming conditions employed, there is an occasion in that there is afforded an light receiving member which is liable to entail an uneven density image on a reproduced image.
It becomes more important to eliminate these defects occurring on the reproduced image as the image-forming speed and detail of the reproduced image increase.
Herein, it should be noted that such defect or unevenness in the deposited film also affects the production of other semiconductor devices.
A principal object of the present invention is to eliminate the foregoing problems in the prior art and to provide a plasma CVD apparatus and process which enable efficiently forming a high quality deposited film having improved characteristics by stably generating uniform plasma while uniformly supplying a high frequency power without localizing the high frequency power and the plasma.
Another object of the present invention is to provide a plasma CVD apparatus and process which enable efficiently forming a high quality deposited film by uniformly growing a film deposited while preventing the occurrence of abnormal film growth and while diminishing the occurrence of the spherical growth defect (which results in entailing a defect such as minute blank area or black dot on a reproduced image) found in the prior art.
A further object of the present invention is to provide a plasma CVD apparatus and process which enable efficiently forming a high quality, highly homogeneous deposited film over the entire surface of a substrate, which is suitable particularly for use in an electrophotographic light receiving member by stably generating uniform plasma without the plasma being localized.
A further object of the present invention is to provide a deposited film-forming apparatus comprising a reaction chamber capable of being evacuated in which glow discharge is caused by means of a high frequency power to form a deposited film on a substrate, wherein said high frequency power is introduced by an insulating material as a base constituent having a region isolated from a glow discharge zone wherein an electrically conductive metallic electrode having a thickness capable of sufficiently transmitting high frequency power is disposed such that it contacts the insulating material.
A further object of the present invention is to provide a deposited film-forming process by introducing a raw material gas and a high frequency power into the above apparatus.